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People take up running, and other types of exercise, mainly to get fit and lose weight. But there's often a social aspect, too. After a gruelling run, some people like to retire to the pub for an ice cold beer.

It can't do any harm ... can it?

If we simply look at numbers, running mainly uses the body's carbohydrate (sugar) and fat stores to provide energy for muscle activity, with the average 70kg person burning approximately 120 calories per mile covered.

A pint of beer or lager contains about 200 calories, so modest beer consumption after a run is unlikely to lead to excessive weight gain. Still, all else being equal, the number of calories in beer means that fairly long distances have to be covered to make up for heavy consumption.

The upside

So, the odd beer after a run is not going to make you fat. But could it also have benefits?

Prolonged exercise results in depletion of the body's liver and skeletal muscle glycogen (sugar) stores. These stores are important to offset fatigue and maintain exercise performance so you don't "hit the wall". As such, high carbohydrate diets are often recommended for ardent exercisers.

During exercise - particularly in the heat - water and electrolytes are lost through sweating. Following exercise, it is important to rehydrate, as well as to supply the body with adequate nutrition to help it recover and adapt.

To achieve this, many take to sports drinks, which contain electrolytes such as potassium and sodium - important for the body's functions - as well as carbohydrates which are used as an energy store.

Despite containing less sodium, beer can in fact be remarkably similar to many sport drinks. So you might ask: why should I not just drink beer instead since it contains many of the beneficial nutrients of a sports drink? There may be downsides...

The catch

The potential downside of having a beer after exercise comes from the alcohol content (most beers are 4-5% alcohol by volume). One problem is that alcohol tends to make you pee more, so it may not be very effective for rehydration and therefore could be harmful for recovery from exercise.

The major organ of the body working during exercise is our skeletal muscles (arms, legs and trunk - about 50% of body weight). Running as an activity can be quite damaging for the muscles and other surrounding tissues, such as bones and tendons.

Jogging home via the pub may help to replace minerals after exercise, but it isn't the best way to re-hydrate. Photo / iStock

As the feet strike the ground, shock waves are sent up the legs creating micro-damage in muscles and surrounding tissues. This is why we feel pain in the hours and days after running and why it can lead to injury.

Yet as we continue training, our muscles should become more resilient to these stresses. So a major concern is how alcohol might affect recovery from exercise and proneness to injury.

When it comes to the liver, the effects of long-term excessive alcohol intake on health, irrespective of exercise, are well documented (development of fatty liver and cirrhosis).

In relation to exercise, the liver is a major glycogen store and, in spite of beer's nutritional value, there is some evidence that alcohol impairs liver glucose storage and release. Once again, these aspects are likely to be detrimental to optimal exercise performance and recovery.

Excessive alcohol consumption can also suppress the ability of muscle to act as a "glucose sink". A major health benefit of exercise is the control of blood sugar, which helps to avoid diabetes. Still, alcohol can oppose the sensitizing effect of exercise on the control of blood-sugar levels.

Also, studies have shown alcohol intake can lead to hormone imbalances. For example, alcohol when coupled to exercise increases catabolic hormones such as the "stress" hormone cortisol, which breaks down muscle.

At the same time, alcohol can decrease anabolic hormones, such as testosterone, which help build up muscle. Longer-term changes in the balance of these hormones can be bad for your health.

So is it OK to have a beer after a run? It is clear alcohol intake - despite its caloric value - can negatively impact responses to exercise. Excessive alcohol consumption could affect aspects of recovery, adaptation and even impact longer-term health benefits of exercise. Still, these conclusions should be placed in context. Existing research linking alcohol consumption to the benefits of exercise remains limited and equivocal.

However, while this is a relatively understudied area, having one or two pints of beer after exercise is likely to have little effect on responses to exercise - unless you are a professional looking for that extra 0.1%! Indeed, in many cases moderate alcohol consumption has been shown to be protective overall, rather than harmful. Everything in moderation.